The present invention relates to a bicycle with a power assisting function, and more particularly to a bicycle with a power assisting function which has a power assisting device comprising an electric motor and is capable of applying part of its energy from extra manual power to charge a power supply of the electric motor for thereby increasing the distance that the bicycle can travel by being assisted by the power assisting device.
There have been proposed vehicles such as bicycles with a power assisting device for assisting in part of the propulsive power with auxiliary power from an electric motor or the like.
For example, a bicycle assisted by an electric motor increases its traction forces when assisted by the electric motor depending on the treading forces applied by the user to the pedals of the bicycle.
Since the rotational output of the electric motor may be transmitted only in a direction to accelerate the bicycle, the rotation of the electric motor is transmitted to the drive wheel via a one-way clutch (freewheel). The one-way clutch is effective to prevent the electric motor from becoming a useless load when the bicycle is run by only manual forces.
The distance that the power-assisted bicycle can travel for a charged quantity of electric energy in a battery on the bicycle is determined by the capacity of the battery and an electric current consumed by the electric motor to assist in running the bicycle.
A example with the following specifications will be described below:
Battery capacity: 5 Ah PA1 Distance traveled by a single battery charging cycle: 30 km
If the bicycle runs 10 km everyday, then the battery on the bicycle has to be charged every 3 days. When the bicycle has run more than 30 km, the bicycle can no longer be assisted by the electric motor. The distance that the bicycle can travel per battery charging cycle is reduced when the bicycle runs uphill and downhill.
As described above, the conventional bicycle with the power assisting function based on the assistive power from the electric motor is disadvantageous in that it cannot travel a sufficient distance per battery charging cycle, needs frequent charging on the battery, and cannot be power-assisted after it has run beyond a certain distance.
FIG. 16 is a block diagram showing a basic arrangement of a conventional bicycle with a power assisting function, and FIG. 17 is a view showing the concept of power transmission of the conventional bicycle. In FIGS. 16 and 17, the bicycle has a crank 1, one-way clutches 2, 6, 10, a treading force detecting circuit 3, an electric motor 4, a speed reducer 5, a crank gear 7, a chain 8, a drive gear 9, a drive wheel 11, a motor drive/output control circuit 12, and a battery 13.
Manual forces applied to the crank 1 are detected by the treading force detecting circuit 3. The motor drive/output control circuit 12 determines an assistive power from the treading forces and the bicycle speed, and controls a current and a voltage of the electric motor 4. If necessary, the motor drive/output control circuit 12 confirms that the voltage and the current are properly controlled. The assistive power is such that it produces the same traction forces as the treading forces up to a bicycle speed of 15 km/h, reduces the traction forces depending on the bicycle speed when the bicycle speed exceeds 15 km/h, and eliminates the traction forces when the bicycle speed is 24 km/h.
The treading forces on the crank 1 are transmitted via the one-way clutch 2 and the treading force detecting circuit 3 to the crank gear 7, and then via the chain 8 to the drive gear 9, from which they are transmitted via the one-way clutch 10 to drive the drive wheel 11, whereupon the bicycle runs in the direction of travel indicated by the arrow in FIG. 17. The output power of the electric motor 4 is transmitted via the speed reducer 5 and the one-way clutch 6 to the crank gear 7, from which it is transmitted in the same manner as with the treading forces from the crank 1. The manual forces and the assistive power from the electric motor are added and applied to the crank gear 7.
The one-way clutch 6 serves to prevent the rotation of the crank 1 from being transmitted to the electric motor 4, so that the manual forces are prevented from being lost when no assistive power is available.
The one-way clutch 2 serves to prevent the rotation of the electric motor 4 from being transmitted to the crank 1, so that the crank 1 is prevented from rotating against the intention of the rider.
In this system, since the electric motor 4 assists in rotating the crank 1 with the intention of the rider, the crank 1 does not rotate against the intention of the rider in principle. However, due to a delay in the detection of the treading forces, the inertia of the rotation of the electric motor, and other processing reasons, the crank 1 may receive rotational power from the electric motor 4. The one-way clutch 2 is required if such rotational power from the electric motor 4 to the crank 1 is not preferable.
The one-way clutch 10 serves to prevent the crank 1 from rotating due to momentum while the bicycle is running. If the one-way clutch 2 is present, then the crank 1 is prevented from rotating without the one-way clutch 10. The one-way clutch 10 is required if a loss caused by the rotation of the chain and the crank gear is not preferable.
The speed reducer 5 comprises a belt or a chain in FIG. 17.
Heretofore, as described above, the one-way clutch 10 is disposed to prevent the drive wheel 11 from rotating the electric motor 4 while the bicycle is running. When the bicycle is propelled, the drive wheel 11 is rotated by the electric motor 4 via the speed reducer. When the bicycle runs due to momentum or in a regenerative mode, the electric motor 4 is rotated by the drive wheel 11 via the speed reducer, amplifying an idling torque of the electric motor 4 and increasing a loss when the bicycle runs without propulsive power. The one-way clutch 10 is provided to avoid such a condition. (If the bicycle were viewed as an ordinary bicycle, it would become heavy when run by only manual forces or it would suffer increased resistance when pushed by the rider while walking.)
If the idling torque of the electric motor is 1 [kg-cm] and the speed reducer has a speed reduction ratio of 1:20, then the torque is amplified to 20 [kg-cm] as viewed from the drive wheel, making the rider feel a very large resistance from the bicycle. The torque of 20 [kg-cm] as converted to traction forces of the drive wheel is equal to about 6 [N]. This makes the rider feel a considerable increase in the resistance because the traction forces required for the bicycle to run at 15 km/h are about 10 [N].
The loss caused by the electric motor comprises a hysteresis loss of iron, a bearing loss, a windage loss, a brush friction loss, etc., with the hysteresis loss and the brush friction loss particularly become a problem.
As described above, the conventional bicycle with the power assisting function has problems in that it cannot travel a sufficient distance per battery charging cycle, needs frequent charging on the battery, and cannot be power-assisted after it has run beyond a certain distance.